In general, the fastener member comprises a rigid skirt that internally forms one or more threads for co-operating with the threaded neck of the reservoir. In order to put the dispenser head into place on the reservoir, it suffices to screw the threaded-skirt fastener member onto the threaded neck of the reservoir.
A first drawback of that screw-fastener member resides in the fact that it is not always easy to determine the torque required to screw the fastener member on the threaded neck of the reservoir in order to obtain appropriate tightness. Another drawback with that screw-fastener member resides in the fact that the threaded skirt of the fastener member need not always come into abutment against the shoulder of the neck at the end of screw tightening. More precisely, the neck of the reservoir generally projects from a shoulder that forms a portion of the body of the reservoir. For appearance reasons, it is advantageous for the bottom edge of the skirt of the fastener member to come into abutment against the shoulder of the reservoir at the end of screw tightening. However, this is not always possible as a result of the shoulder not always being situated at the same distance from the threads of the neck. Consequently, at the end of screw tightening, it often happens that a gap remains between the bottom edge of the skirt of the fastener member and the shoulder of the reservoir. Not only is this unattractive, but it also leads the user to believe that the dispenser head is not properly mounted on the reservoir. Finally, mounting a screw-fastener member requires the use of a special mounting machine that generates controlled turning.